The present invention relates to a stress evaluation method using acoustic waves and an apparatus therefor which is capable of evaluating stress acting on a test piece under inspection.
It is well known to use acoustic waves to obtain a magnitude of stress acting on the test piece on the basis of changes in acoustic velocity.
Namely, according to a prior art method which uses a relationship obtained in advance between a ratio of changes in acoustic velocity and stress values, a magnitude of stress acting on a particular point can be obtained from the acoustic velocity measured at that point.
The stress evaluation method using a surface wave for evaluating stress present in the surface layer of the test piece has been disclosed, for example, in JP-A-61-254849.
Further, there is a method to obtain a measure of internal stress in the test piece as an average value from a difference in acoustic velocities between a shear wave which oscillates in the parallel direction relative to the stress and a shear wave which oscillates in the orthogonal direction relative to the stress, as disclosed in JP-A-56-90228.